Piston for internal-combustion engines



S. L. G. KNOX PISTON FOR INTERNAL COMBUSTION ENGINES W 6 3 I. Z J 0 3 5 J L A Z w L 6 l /7 o 7* l w n w 0r 0 4 .7 NZ m J w 3 I" Z M d u .1 r F. a J 9,0, m 7 1.. "i 6 O T, 1 8 a m My.

INVENTOR 5, 6; Knot A TTORNE Y5 Patented fiat. 6, 1925.

SAMUEL LIPPINCOTT GRISWGLD KNOX, OF NEW YORK, N. Y.

PISTON FOR INTERNAL-COMBUSTION ENGINES.

Application filed May 24, 1922.

To all whom it may coma-"m:

Be it known that I, SAMUEL LIPPINCOTT Gnrswonn Knox, a citizen of the United States, residing at 32 West lOth Street, in the county of New York, State of New York, have invented certain new and useful Improvements in Pistons for Internal-Combus tion Engines; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The present invention relates to internal combustion engines and more particularly, it is directed to the construction of the piston and cylinder of an internal combustion engine in such manner as to increase the efficiency of the engine by reducing the losses caused by the rubbing of the piston upon the walls of the cylinder. As the result of an investigation carried on for the purpose of determining the principal causes of rubbing losses in internal combustion engines, it was found, not only that a very large portion of the total engine rubbing losses occurs between the walls of the cylinder and the piston, but also that the greatest part of this piston friction is caused by the adhesion between the surfaces of the piston and the cylinder walls. rather than by mechanical pressure against the walls chargeable to the transverse component of the connecting rod forces, and to the sealing rings. So large is this loss that it has been found in some cases to approximate that of all of the other sources of engine frictional losses added together. This result is thought to be largely attributable to the fact that the film of oil presenttends to increase the adhesion'between' the surfaces of the piston and cylinder, and to the fact that the motion of the piston is a reciprocating motion, the piston coming to rest at each end of its stroke and having to be set in motion'against static friction which is greater than sliding friction. The adhesion caused by the film of lubricating oil may possibly be explained by the fact that the lubricating oil is always to acertain extent carbonized in part by the escape of a small quantity of burning gases past the sealing rings, and in part by the exposure of the cylinder walls to the temperature of the burning gases. This car bonization contaminates the oil and renders it more viscous, and increases its resistance to shear.

Serial No. 563,275.

also been reduced by cutting away the sides of the skirt below the rings, leaving only two roughly triangular surfaces to take the reaction of the side thrust of the connecting rod on the gudgeon pin.

However, in some engines it is necessaryto employ a longpiston, that is, a piston the length of which, including that portion required to carry the packing rings, is greater than the length of the stroke of the engines.

Thus in engines of the twostroke cycle type, having ports in the cylinder walls near the outer end of the stroke, or in any type of engine having ports so placed, whether for exhaust. inlet or scavenging, it is customary to have a skirt on the piston which serves the function of a valve, to seal the above referred to ports. The skirt must have a cylindrical surface continuous throughout a length somewhat greater than the stroke of the engine, or, if no such, continuous cylindrical skirt is provided, some corresponding means must be employed. Because of the very large skirt necessary in this type of engine for the purpose of maintaining the ports closed while the piston is above the same, the frictional losses are extremely high on account of the relatively large area of contact presented for adhesion between the moving surfaces of the piston and cylinder. It is the object of my present invention to provide means for decreasing-these losses in engines of this type.

In carrying out the invention, a circumferential section of relatively short length and slightly smaller in diameter than the cylinder is preferably provided on the inte'rior walls of the cylinder near its outer end, and one or more ports are provided in spaced relation to this circumferential section. The long piston which is adapted to reciprocate in this cylinder has a sealing ring portion which slides in rubbing contact With the walls of the cylinder and which is of a length which is not greater than the spacing of the ports from the circumferential section. The piston has a skirt portion of iieduced diameter which slides in rubbing contact with the circumferential section and the difference in diameter between the skirt portion and the cylinder walls serves to break the oil film but does not form a chamber therebetwcen In this way the area of the relatively moving surfaces which are in rubbing contact with one another is greatly reduced, thereby proportionally reducing the tendency for adhesion and consequently the piston frictional losses. At the same time however, the control of the cylinder ports is just as effectual as though the piston were of full diameter throughout its entire length.

Several embodiments of my invention are illustrated in the accompanying drawings in which;

Fig. 1 indicates diagrammatically an engine of the two-cycle type embodying my invention;

Fig. 2 is a diagrammatic view showing my invention applied to a two-cycle engine having double opposed pistons;

Fig. 3 is an enlarged sectional view of a portion of the cylinder and piston shown in Fig. 1 or 2;

Fig. t is a similar view of a cylinder and piston, the sealing rings cooperating with the skirt portion of the piston being omitted,

Referring to Fig. 1 of these drawings the engine cylinder is indicated at 5 and is provided with a piston 6, which is connected with the crank shaft of the engine in the ordinary manner. In the top of the cylinder 5 there is located the inlet valve 7, which is operated by any suitable means, to admit air or fuel at the proper time, the air or fuel being supplied to the engine through the opening 8. The exhaust ports 9 are provided in the lower part of the cylinder 5 and may be disposed around the circumference of the cylinder. These ports communicate by means of the annular passage 10. with the exhaust opening 12. These exhaust ports are controlled by the piston 6, and will be opened when the top of the cylinder passes below them, and closed at all other times.

The piston 6 is provided at its upper end with a. relatively short section 13, in which the packing or sealing rings 14 are carried. This sealing ring section is of suitable length for the packing rings and is made as short as is compatible with due allowance for such side thrust as may exist, and for wear. The. skirt section 15 of the piston is of slightly less diameter than the sealing ring section 14 and the cylinder 5, so that it does not make contact with the internal working surface of the engine cylinder. The diameter of the pistol! is t?- lieved throughout its skirt portion to break the oil film between the surfaces of the skirt and the cylinder. At the lower end of the cylinder, there is provided on the interior thereof a relatively short circumferential section 16, which is of suitable diame-.

ter to form a sliding fit with the skirt 15 of the piston. The purpose of this section 16 is to prevent leakage past the surface of the skirt and to serve as a guide to preserve the alignment of the piston. Sealing rings 17 may be provided in section 16, if desired.

It will thus be seen that when the piston is caused to reciprocate in the cylinder, the only rubbing surfaces between the piston and cylinder are those constituted by packing ring section 13, plus the relatively short section 16 which cooperates with the skirt of the piston. The unnecessarily long rubbing length of the pistons now in common use is eliminated. The piston, however functions in the same manner, as far as the working cycle of the engine is concerned as the ordinary engine piston having a skirt of the same diameter as the cylinder, the ports 9 being opened when the top of the cylinder passes below them, and being kept closed while the piston is accomplishing the com ression and working parts of the cycle. By the skirt portion 15 which slides in rubbing contact with the relative ly short circumferential section 16.

Referring now to Fig, 2, there is here shown an engine of the two-stroke cycle double opposed piston type. The cylinder is indicated at 18 and the pistons at 19. One of these pistons is' connected through the cross-head 2'0 and the connecting rod to the crank 23. The opposite piston is connected by piston rod 2 1 to the cross-head 25, this cross-head being connected. through two side rods 26 with their corresponding cranks 27. The pistons 19 are constructed s milar to the piston 6 of Fig. 1 that is, they are provided with relatively short sealing ring sections 28. and skirt sections 29, the skirt sections being of slightly less diameter than the sealing ring sections so as to break the oil film between the surfaces of the skirt and the cylinder. 7

The outer ends of thecylinder 18 are provided with relatively short sections 33 which are of suitable diameter to form a sliding fit with the skirt sections 29 of the pistons. These sections 33 may be provided with sealing rings 34, if desired.

This type of engine is provided with a circumferentially disposed row of inlet ports 30, and a circumferentially disposed row of exhaust ports 31. These ports are controlled by the operation of the pistons 19. Then the pistons 19 are in the position shown in Fig. 2, the scavenging air, or fuel, is being admitted, under suitable pressure,

through the ports 30, and is clearing the cylinder of the burned gases which are passing out of the exhaust ports 31. \Vhen, however, the pistons 19 move toward each other for the compression stroke, they close the ports 30 and 31, and maintain them closed during the compression and working strokes following, because the length of the pistons 19 is greater than the length of the stroke of the engine.

It will be seen that here again the length of the rubbing surfaces between the pistons 19 and the walls of the cylinder 18 is reduced to the combined lengths of the packing ring sections 28 and the relatively short sections 33.

In Figs. 3 and 4, the relative diameters of the skirt, section and the sealing ring section of a piston constructed according to my invention have been greatly enlarged, beyond what is really necessary, in order to show the invention more clearly. In Fig. 4-, the section 16 of Fig. 1, or 33 of Fig. :2, is shown without sealing rings.

By this construction of the piston and cylinder, the friction of engines which must necessarily be provided with long pistons, is greatly reduced. The bearing surfaces between the piston and cylinder can be designed so as to be of the proper size for the duty required and do not have to be made too large for their work, as is the case in engines in present use.

I claim:

1. In combination, a piston, an engine cylinder having a port near its outer end which is controlled by the pison, the piston being provided with a relatively short sealing portion of full diameter and a skirt portion reduced in diameter sufficiently to break the oil film between it and the cylinder walls but without providing a chamber therebetween, and a relatively short circumferential section on the cylinder, below the ports, adapted to coact with the said skirt portion to form sealing means therewith. I

2. In an engine, the combination of a cyl' inder having a port in the walls thereof, ,a cooperating piston therefor controlling the opening and closing of said port, a skirt portion on the piston for maintaining the port closed during a portion of the movement of the piston, said skirt portion being reduced in diameter throughout its entire working length by an amount which is just sufiicient to break the oil film between itand the cylinder walls.

3. In an engine, the combination of a cylinder having a port in the walls thereof, a cooperating piston therefor controlling the opening and closing of said port, a skirt portion on the piston for maintaining the port closed during a portion of the movement of the piston, said skirt portion being reduced in diameter throughout its entire working length by an amount which is just suflicient to prevent adhesion between it and the cylinder walls.

4. In an engine, the combination of a cylinder the walls of which are provided with a circumferential section of reduced diameter and a port spaced therefrom, and a long piston adapted to control the port and having a ring portion in rubbing contact with the cylinder and a skirt portion of smaller diameter than the cylinder and in rubbing contact with said circumferential section, the length of the ring portion being not greater than the spacing of the port from the circumferential section, and the difference in diameter between the skirt of the piston and the cylinder walls serving to break the oil film but not forming a chamber therebetween so that the port is kept closed while the top of the piston is above the same.

In testimony whereof I aflix my signature.

SAMUEL LIPPINCOTT GRISWOLD KNOX. 

